Field of the Invention
This invention relates to a method and apparatus for generating high contrast, high resolution images, with or without enlargements. More specifically, this invention relates to a method and apparatus for generating video or digitized images in two or three dimensions and a spectacle mounted display. When used in conjunction with a digitally enhanced imager for people with a vision impairment, visual information of various spatial frequencies, contrast, and wave length can be selectively enhanced and projected into a person's eye to compensate for the visual impairment.
The device can produce stereoscopic three dimensional images because each eye gets a separate image. Images can be in black and white or color.
An image can be described by contrast, spatial frequency, resolution and wave length. Contrast is defined as the difference in intensity or brightness between the light and dark areas of the image. The spatial frequency is defined as the inverse of the angular separation between component lines which make up an image. The resolution is the angular subtense of the smallest point visible to the observer. The wave length of visible light extends from 380 nm for violet-blue to about 750 nm deep red.
Individuals with impaired vision have vision that is contrast dependent. The ability of a person with a visual impairment to properly perceive an image is dependent on the contrast of the image. Many times people attempt to read a magnified image and they report it looks bigger but not clearer. Increasing brightness of the text and increasing the darkness of the background makes the print more legible even if the print size remains the same.
In addition to contrast, the resolution of an optical or electro-optical system will determine its visibility. Resolution is defined as the minimum angular separation of the details of a character. For example, the letter E can be made more legible by increasing the contrast between the spaces and the lines of the letter. In general, the sharper the delineation between the text and the background, that is, the narrower the width of the transition area between the text and the background, the higher the resolution and the sharper the image. In addition, studies of individuals with impaired vision have shown that increased spacing between characters also enhances readability.
In a conventional analog video display system, which includes a camera, monitor, transmitter and receiver, the image is limited by the contrast, spatial frequency and resolution of the objects whose images are being captured and transmitted by the camera. The image is further limited by the resolution of the video display device such as a monitor. The contrast in the image cannot be modified between discrete portions of the image such as brightening a light background and darkening dark letters; nor, can the visibility be enhanced by substantially reducing the transition between light and dark areas in the image on the monitor. This problem of visibility is aggravated when the images are enlarged substantially, a frequent requirement for improving readability of text for individuals with impaired vision.
There are also numerous devices which use digitized video images but these are primarily directed toward compressing the information into a narrow band width such as described in U.S. Pat. No. 4,394,774 Widergren, which describes a digital video compression system directed at NTSC color broadcast compression and expansion systems or in U.S. Pat. No. 4,772,956 Roche, which also is directed at a video transceiver including a compressor to reduce the time required to transmit and digitize a video frame over a narrow band width channel.
Neither of the inventions described in Widergren or Roche or other inventions such as that described in U.S. Pat. No. 4,689,741 Redwine, which is directed at memory devices designed to reduce or prevent the transfer of spurious or non-valid signals from the video storage circuit to the video display device or processor are designed to enhance contrast or resolution.
There are numerous devices which have been used to enhance and enlarge images in the prior art.
Closed circuit video has been used as an adaptive device for individuals with impaired vision for the past twenty years with only minor modification. Appollo Laser, Sun Chemical, Visual Tech, and more recently Telesensory and Enabling Technology all have used this technology to enlarge print. As indicated previously, simply enlarging print does not mean enhanced visual performance for many individuals with impaired vision.
A standard video image such as that displayed on a television screen is composed of 525 lines disposed from top to bottom which are scanned horizontally at 15.75 KHz. The electron beam which creates the image scans every other line and then returns to fill in the skipped lines. The first half of the lines (262.5) is scanned in 1/60th of a second, followed by the second half in the next 1/60th of a second. The interlaced scanning reduces flicker. Thus, each frame which is made up of the 525 lines is scanned in 1/30th of a second at a rate of 15.75 KHz. The three widely used standards, including the Monochrome RS-170, NTSC and European PAL, are all essentially equivalent for the purposes of the present invention.
Modern video signals have not changed much since the Iconoscope, which was first described in 1923 by Vladimir Kosma Zworykin. Mr. Zworykin received a patent for this device in December, 1938. Subsequently RCA patented a picture tube called a kinescope.
For a video image to be formed on a picture tube two conditions must be met. First, the beam striking the screen must be able to release more light as the voltage of the video signal increases. Second, the electron beam of the camera and the picture must scan at the same rate. These scan rates are locked together by a sync pulse that is embedded in the video signal that occurs at the end of every line. By digitizing the image and increasing the scan rate as embodied in this invention the resolution of the image can be enhanced. By digitizing the image and using comparators and digital filters the contrast and spatial frequencies can be enhanced. This significantly improves the image quality beyond the prior art. High resolution, high speed displays, including flat panel displays (Fuanda et al., Ishii et al., Masit et al., Orceyre (Fr)), that do not use an electron gun to create the image, are capable of displaying high scan rate video images. A further advantage of flat panel displays are their light weight and thin compact shape which makes them readily portable.
There is nothing in the patents previously cited, nor, in other areas of the art, directed toward contrast and resolution enhancement to improve the recognition of images, by individuals with impaired vision in real time processes.